1. Field of the Invention
The present invention relates to iris color and, more particularly, is directed to the measurement of changes of iris color over time with diseases and the use of drugs.
2. Description of the Prior Art
The pattern of iris color and its pigmentation varies greatly between individuals and can change throughout life and with disease. There appears to be changes in iris color for some persons from 6 years of age to adulthood. Iris color has been associated with several diseases such as macular degeneration increased ocular pressure, diabetes mellitus, vascular hypertension, and lens density.
Furthermore, the color or pigment of the iris can change with drug therapy. Recently, studies have found a change in iris color with ocular medications such as latanoprost and unoprostone.
Most of the studies evaluating iris color have used subjective methods either direct assessment by the observer, the use of iris photographs as a reference standard and the use of glass eye anterior segments. Apparently, when iris photographs were used, they were not taken in a standardized manner, but rather with different films and exposures. At present, an available method for measuring the iris for identification purposes is the use of texture of the iris and not the color or pigment.
Two attempts at developing objective methods measuring iris color have been described recently. However, neither one measures the changes of iris color over time. One attempt used standardized setting for slit lamp photographs for obtaining a photograph which provides an evenly illuminated image of one iris quadrant. A standardized color scale was used as a reference with the caps of a Farnsworth-Munsell 100 hue test. Another attempt used a spectroradiometer calibrated on measurements of a set of 72 artificial irides to measure standardized color coordinates.
It would be advantageous to have a standardized photographic technique to obtain iris photographs and to use an objective method for measuring area and density of color of the iris over time.
The prior art teaches methods for standardized illumination and for controlling pupil size. U.S. Pat. No. 4,641,349 discloses a method for obtaining an image of the iris and measuring it for comparison to a previous image of the iris for identification purposes. U.S. Pat. No. 5,291,560 discloses a method for obtaining images of the eye and iris for identification purposes using the texture of the iris. Measurement of the texture of the iris is accomplished by digital analysis of algorithms of the iris. An xe2x80x9ciris codexe2x80x9d was used to confirm the identity of any individual. Both of these patents do not provide methods for measuring change of iris color over time either from diseases or the use of drugs. These patents do not correlate the use of the ratio of the different colors from the measurement of a series of images of the iris taken over time.
It is an object of the present invention to provide a method for measuring the change of iris color over time.
It is another object of the present invention to measure changes of iris color over time as a result of disease and/or the use of drugs.
In the present invention, computerized image analysis was applied to measure area and density of iris color and to determine changes of iris color using photographs taken over time. First, color slides are digitized in the Red-Green-Blue (RGB) spectrum (Whitelight). A region of interest (ROI) was then selected so that artifacts such as corneal reflection can be minimized. Perceptual color components of hue, saturation and luminance are then computed from RGB color space. The exposure level is corrected using controlled surface area. A color ratio is computed from RGB color space such as red/blue. As a preprocess, color is enhanced and background noise is kept minimum. Enhancement of iris color is done using receptive field filters. Segmentation of iris color is carried out by squashing function parameters. A binary mask was applied to characterize segmented iris color. Pairs of images of the same iris taken at different times are transformed onto the same Cartesian-coordinates so that characteristics of iris features locate identical topographic position if there is no iris color changes. Image texture is quantitated using spatial Gray-Level Dependence Matrices. Finally, for these class regions with characteristic optic density pattern, changes over time for iris color are defined by regression analyses of slopes and correlation analyses as well as the difference of the final measurement minus initial measurement.
Two initial studies were done on 30 normal subjects followed for a mean of 10.1 months with photographs taken at baseline and 6.5 months after baseline and then 3.6 months after the first follow-up visit. Percent coefficient of variation of duplicate measurements for area of color ranged from 4.04 to 5.83% and for density of color from 1.79 to 2.73%. The percent difference of the measurements between the first and second follow-up visit from baseline ranged from 1.2 to 6.3%. A third initial study was done on 23 glaucomatous eyes treated with prescription eye drops, for example, latanoprost eye drops sold by Pharmacia under the trademark Xalatan, followed with iris photographs about every four months for three years. Using the ratio of red/blue was superior to the white light method for spread of change of mean values over time even though the reproducibility of the two methods were similar. There were also significant correlations of the slopes of the measurements over time of the red/blue method with other methods to evaluate the trend or change of iris color over time. Furthermore, with the red/blue method, normal subjects show no changes in iris photographs over 10.1 months of follow-up.